This invention relates to a so-called laminated magnetic head and, more particularly, to improvement in electro-magnetic transducing characteristics in the laminated magnetic head.
In a magnetic recording/reproducing apparatus, such as a video tape recorder (VTR), attempts are being made for increasing the density and the frequency of recording signals. In keeping up with such attempts, a so-called metal tape employing magnetic metal powders, such as Fe, Co or Ni powders, and an evaporated tape, in which a magnetic metal material is directly deposited by evaporation on a base film, are being used in increasing numbers.
Since this type of the magnetic recording medium has high residual magnetic flux density Br and high coercivity Hc, it is demanded of the material of the magnetic head employed for recording and playback to have high saturation magnetic flux density Bs and high permeability.
In keeping with the tendency towards high density recording, attempts are being made to narrow the recording track width on the magnetic recording medium and accordingly an extremely narrow track width of the magnetic head is required.
Thus a so-called laminated magnetic head has been proposed, in which magnetic core halves comprising a magnetic core film sandwiched between a pair of non-magnetic substrates are abutted to each other with the end faces of the magnetic core films facing each other, with the interface between the magnetic core films defining a magnetic gap. With the laminated magnetic head, since the substrates on either sides of the magnetic core film are of the non-magnetic material, the track width is determined by the film thickness of the magnetic core film. Thus the track width can be narrowed easily by controlling the film thickness of the magnetic core film.
Meanwhile, since magnetic permeability within the film plane of the magnetic core film directly influences the performance of the magnetic head, it is crucial to control the state of magnetization of the magnetic core film surface in order to improve electro-magnetic transducing characteristics of the magnetic head.
According to the results of analyses of the magnetic path, as reported in Extended Abstract of the 11th Meeting of the Society of Applied Magnetic Engineering of Japan, it is necessary that the relation .mu.x&gt;.mu.y be met, where .mu.y, .mu.x stand for the magnetic permeability in a direction parallel to the gap depth within the film surface of the magnetic core film and the magnetic permeability in a direction normal to the gap depth, respectively.
In order for the relation .mu.x&gt;.mu.y to hold, it suffices if the gap depth direction is the easy axis of magnetization.
However, with the laminated head for high density recording, the gap depth and the track width are narrow and on the order of tens of .mu.m. The magnetic gap having such narrow gap depth and track width exhibits shape anisotropy which renders the gap depth direction into the direction of hard magnetization. Thus the diamagnetic field becomes extremely strong when the magnetization is oriented along the gap depth.
Consequently, even if anisotropy is applied so that the easy axis runs parallel to the gap depth, the magnetic domain structure is significantly affected by shape anisotropy, if the applied anisotropy is relatively small, as a result of which the easy axis is oriented in a direction normal to the gap depth, and hence the relation .mu.x&gt;.mu.y does not hold, as shown in FIG. 1, showing the gap portion of the magnetic head defining a closed magnetic path by a pair of magnetic core halves 121, 122 to an enlarged scale.
On the other hand, if anisotropy applied in a direction parallel to the gap depth direction is larger, there is generated, due to the demagnetizing field produced under the effects of the shape anisotropy, a triangular magnetic domain 123 is generated which minimizes the magnetic energy within the magnetic core film, as shown in FIG. 2. Although the relation .mu.x&gt;.mu.y holds in such case, the triangular magnetic domain is of such a cyclic structure as to close the magnetic flux within the film plane, and does not lead to improved .mu.x. On the other hand, since the magnetic permeability along the difficult axis is inversely proportional to the magnitude of anisotropy, the value of .mu.x itself becomes small if the anisotropy applied is of too large a magnitude.
Thus, with the laminated magnetic head having narrow gap depth and narrow track width, the playback efficiency cannot be improved sufficiently if anisotropy ia simply afforded so that the gap depth direction is the easy axis, such that it is difficult to improve electromagnetic transducing characteristics in the high frequency region.